Heat-sealable films are widely used in packaging applications for consumer items such as snacks, bakery over-wrapping, confectionary, etc. Heat-sealable films can be oriented polymeric films, such as biaxially oriented polypropylene (BOPP) films. Heat-sealable BOPP plastic films are known from, for example, U.S. Pat. Nos. 8,431,234; 5,489,454; 4,996,096; and US Pub. 2012/0258307. In heat-sealable food packaging, there is an outer layer which is intended to come in contact with the food and which is heat-sealable. The heat-sealing is typically carried out using a heat sources such as electrically-heated metal bars which are provided of a pneumatic or hydraulic closing system. Once the film has been folded onto itself to bring two edges of the covering layer in contact with one another, the film is clamped between heat-sealing bars, so that it can be submitted to the simultaneous action of temperature and pressure leading to welding of the edges and closure of the packaging.
The seal must have the characteristic of exhibiting a very high sealing strength so as to ensure a high integrity in the closure of the packaging. This high sealing strength of the weld, which ensures proper preservation of the contents during transport, storage, and display, unfortunately requires a correspondingly high force to separate the joined layers to open the package. So once the weld gives and the package opens, the force applied continues to be exerted on package walls. As a result, there is often uncontrolled breakage of the package, resulting in the packaging being opened more rapidly and/or being opened more completely than desired.
A number of prior patent publications such as U.S. Pat. No. 5,773,136 by Alder et. al.; U.S. Pat. No. 7,316,848 by Longmoore; US H1727 ('727) by Jones et al.; and EP 1810823 ('823) by Filippo et al. have proposed heat-sealable films which are also peelable. In these constructions, one layer of a multilayer film has a composition such that it can be peeled from the adjacent layer. That is, the peelable layer has a sealing strength with respect to its adjacent layer which is a lower sealing strength than that between two heat-sealed edges.